In my office, we had a terrible fruit fly break out. No clue where they were coming from, but there were dozens and dozens over just a week.
We filled some Tupperware containers with vinegar and put holes in the top just barely big enough for them to get in. Next day, there were hundreds of dead flies in the traps throughout the office.
I'm not sure about how they're getting in, but it sounds like there's something decaying that is attracting them. Here is some advice to getting rid of the ones that are already there.
How to kill a fly without a flyswatter.
In three easy steps
1.) Position your hands a few inches above the fly as if you were about to clap.
2.) Clap.
3.) Wash hands.
Conservatism is not about leaving people behind. Conservatism is about empowering people to catch up, to give them tools at their disposal that make it possible for them to access all the hope, all the promise, all the opportunity that America offers. - Marco Rubio